Hardman U.S. Par. No. 2,837,519, June 3, 1958, described the reaction of 2-(morpholinothio)benzothiazole, sulfur and morpholine in ethanol to produce morpholinodithiobenzothiazole. Morpholine is referred to as a catalyst, but is used in molecular amount and attempts to reduce the dosage have proved unsuccessful. However, there has now been discovered materials which promote the reaction in catalytic amounts. The same product forms from reaction of 2,2'-dithiobis(benzothiazole) and N,N'-dithiobis(morpholine) which reaction is promoted by amines, Hardman U.S. Pat. No. 3,086,018, April 16, 1963, but substantial amounts are needed to achieve reasonable acceleration of the reaction as reported by D'Amico U.S. Pat. No. 3,489,754, Jan. 13, 1970, who found that the exchange reaction is catalyzed by certain alkali metal salts. This invention is concerned with improvements in the sulfur insertion reaction.